Micro-electromechanical systems (“MEMS”), fabricated using standard VLSI semi-conductor chip fabrication techniques, are becoming increasingly popular as new applications are developed. Such devices are becoming widely used for sensing (for example accelerometers for automotive airbags), inkjet printing, micro-fluidics, and other applications. The use of semi-conductor fabrication techniques allows MEMS to be interfaced very readily with microelectronics. A broad survey of the field and of prior art in relation thereto is provided in an article entitled “The Broad Sweep of Integrated Micro-Systems”, by S. Tom Picraux and Paul McWhorter, in IEEE Spectrum, December 1998, pp 24-33.
In PCT Application No. PCT/AU98/00550, the entire contents of which is incorporated herein by reference, an inkjet printing device has been described which utilizes MEMS processing techniques in the construction of a thermal-bend-actuator-type device for the ejection of a fluid, such as an ink, from a nozzle chamber. Such ink ejector devices will be referred to hereinafter as MEMJETs. The technology described in the reference is intended as an alternative to existing technologies for inkjet printing, such as Thermal Ink Jet (TIJ) or “Bubble Jet” technology developed mainly by the manufacturers Canon and Hewlett Packard, and Piezoelectric Ink Jet (PIJ) devices, as used for example by the manufacturers Epson and Tektronix.
While TIJ and PIJ technologies have been developed to very high levels of performance since their introduction, MEMJET technology is able to offer significant advantages over these technologies. Potential advantages include higher speeds of operation and the ability to provide higher resolution than obtainable with other technologies. Similarly, MEMJET Technology provides the ability to manufacture monolithic printhead devices incorporating a large number of nozzles and of such size as to span all or a large part of a page (or other print surface), so that pagewidth printing can be achieved without any need to mechanically traverse a small printhead across the width of a page, as in typical existing inkjet printers.
It has been found difficult to manufacture a long TIJ printhead for full-pagewidth printing. This is mainly because of the high power consumption of TIJ devices and the problem associated therewith of providing an adequate power supply for the printhead. Similarly, waste heat removal from the printhead to prevent boiling of the ink provides a challenge to the layout of such printhead. Also, differential thermal expansion over the length of a long TIJ-printhead may lead to severe nozzle alignment difficulties.
Different problems have been found to attend the manufacture of long PIJ printheads for large- or full-page-width printing. These include acoustic crosstalk between nozzles due to similar time scales of drop ejection and reflection of acoustic pulses within the printhead. Further, silicon is not a piezoelectric material, and is very difficult to integrate with CMOS chips, so that separate external connections are required for every nozzle.
Accordingly, manufacturing costs are very high compared to technologies such as MEMJET in which a monolithic device may be fabricated using established techniques, yet incorporate very large numbers of individual nozzles. Reference should be made to the aforementioned PCT application for detailed information on the manufacture of MEMJET inkjet printhead chips; individual MEMJET printhead chips will here be referred to simply as printhead segments. A printhead assembly will usually incorporate a number of such printhead segments.
While MEMJET technology has the advantage of allowing the cost effective manufacture of long monolithic printheads, it has nevertheless been found desirable to use a number of individual printhead segments (CMOS chips) placed substantially end-to-end where large widths of printing are to be provided. This is because chip production yields decrease substantially as chip lengths increase, so that costs increase. Of course, some printing applications, such as plan printing and other commercial printing, require printing widths that are beyond the maximum length that is practical for successful printhead chip manufacture.